What is the influence of infill %, layer height and infill pattern on my 3D prints?

Improving the mechanical performance of a printed part often comes at the expense of printing speed, affordability and quality. In this study we quantify the impact of different parameters on performance, and we try to help users choose the optimal settings by clearly laying out the trade-offs faced by the user. We provide the settings we would pick depending on the application requirements.

The key parameters we look into are infill %, layer height and infill pattern. In the main body of this study, we provide a detailed description of the influence these parameters have on max stress, elongation at break, rigidity (Young Modulus) and yield stress.

Key findings

To best sum up the large amount of data we gathered, we present the user with the table of preferred settings we would choose, depending on the application requirements. Does your print need strength or quality? Are you trying to minimize cost or are you trying to save time? Or is it – as is often the case – a combination of these requirements?

These conclusions are based on our interpretation of the trade-offs presented in the following tables:

The Strength, Speed and Cost tables were extrapolated from the mechanical tests we made[1]:

Strength corresponds to the maximum stress the specimen can take before breaking

Speed describes the printing time of a specimen

Cost is derived from the actual weight of the specimen, and assumes 30€/kg

Quality relates to the general aspect of printed parts based on their layer height[2].Quality is not the focus of this study but the relationshipbetween quality and layer height is generally accepted[3].

A much more detailed analysis of the mechanical tests is provided in the rest of the study. In particular, we show that elongation at break is lowest around 90% infill, which is not necessarily intuitive. Although elongation at break is not part of the requirements presented in the tables above, it could influence the decision on the settings the user ends up choosing.

The other key parameter we looked into was infill pattern. We show that generally, the best patterns to use are Linear or Diagonal (=Linear tilted 45°).

Indeed, decorative patterns such as Moroccan stars and Catfill show poor performance and should only be used if they are exposed and are part of the design. The real debate was between Linear, Diagonal and Hexagonal (a.k.a. Honeycomb).

At a low infill %, we show that all three are fairly equivalent. Because Hexagonal is more demanding on the printer (more directional changes), we suggest using Linear or Diagonal.

At a high infill %, Hexagonal is essentially the same as Linear and therefore the discussion is really between Linear and Diagonal. We show that Diagonal is ~10% stronger than Linear.

Finally we made a test on the anisotropy of a 3D printed part: this means that 3D printed parts are weaker along the Z-axis than they are along the X and Y-axis. We show that the parts are 20% to 30% weaker along the Z-axis, and that elongation at break is about half.

About the testing procedure

For each specimen we tested, we measured the following mechanical properties:

Max stress (Ultimate Tensile Strength)

Elongation at break

Young modulus (Rigidity)

Yield stress

The material used is PLA, and the 3D printing process is Fused Deposition Modeling (FDM). The three parameters we studied are:

Infill %: percentage of the object’s volume (inside) that is filled with material

Layer height: thickness of each layer constituting the object

Infill pattern: pattern the nozzle is drawing to fill the object

We performed the tensile tests with a universal testing machine, at the PIMM lab of Arts et Métiers Paristech. We aggregated the results and chose to display the tables and graphs we think are most relevant.

The characteristics of PLA are well-known when the material is formed by injection molding. The point of this study is to better understand its behavior once it has been 3D-printed with the FDM process. To give a point of comparison, here are the characteristics of injection molding PLA[4]:

Strength [MPa]

40 – 70

Elongation at break

4% – 6%

Young modulus (rigidity) [GPa]

2 – 4

Detailed results: Infill % test

We printed specimens with the following infill %: 10, 30, 50, 70, 90, and 100. The other printing parameters are:

Printer: MakerBot Replicator

Speed: 60mm/s

Layer height: 0.20mm

Temperature: 195°C

Infill pattern: Linear

Number of shells: 2

We tested three specimens for each infill %

Considerations on strength

Unsurprisingly, the specimen strength increases with infill %, from 10MPa at 10% to 46MPa at 100%. However, it is interesting to note that the evolution is not linear: the strength gained per percentage point of infill also increases. To put it another way, reducing infill from 100% decreases resistance less and less.

Increasing infill % means a higher amount of material is used (= higher cost) and printing time is longer. This has several interesting consequences on ratios such as [strength / speed] and [strength / weight]:

The graph on the right shows that the 30% to 50% range is least efficient from both cost (material usage) and printing time standpoints, as they have the lowest ratios.

Other performance results

Elongation at break:

The most surprising result of this study probably lies in this test. Elongation at break is remarkably constant around 2.8%, except at 90% infill where it drops to 2.0%. We checked that there had not been an error by testing another batch of two specimens for infill % 80, 90 and 100, and the results are as follows:

This second test confirms the drop around 90% infill.

Our hypothesis is the following:

For infill below 80%, the extruded PLA filaments constituting each layer (we will just call them “filaments”) do not touch each other along the specimen axis: there are clear gaps in the mesh. So the filaments can elongate in parallel the same amount before breaking, regardless of infill%.

For infill around 90%, the filaments touch and form a continuous 3D material, but it is porous because there are lots of small air voids in it (~10% of the specimen). In this case, the stress concentrates around the voids so the strain is localized around the void areas. The voids behave like faults that expand to eventually join and break, but lead to a lower elongation at break. This seems to be confirmed by the fact that the break is slanted for 90%, while it is straight for 70% or 100% (see picture below).

For 100% infill, the plastic filaments also touch but there are (nearly) no more air voids in the material. Therefore the plastic deformation is not localized anymore and the whole specimen behaves as a single plastic filament would. Therefore we find the same elongation at break as the case where filaments elongate in parallel (below 80% infill).

This point deserves a more in-depth analysis to confirm our hypothesis.

Yield stress:

Yield stress increases from 8 MPa at 10% infill to 28 MPa at 90% infill, before decreasing back to 23MPa at 100% infill. The fact that yield stress is higher at 90% than at 100% infill is in line with our hypothesis on elongation at break: the stress is localized around the air voids at 90% so at a macro level, the material yields at a higher stress.

Young modulus (rigidity):

Because the specimen is porous (except at 100%), there are two ways to calculate rigidity:

We can count the void inside as part of the material and calculate the Young modulus by dividing by the full cross-section.

Or we can adjust the calculation by multiplying the cross-section area by the infill %.

The non-adjusted curve shows a positive and linear relationship between infill % and rigidity. Consequently, the adjusted curve is mostly constant around 3.0GPa, right in the range of PLA’s rigidity (see section About the procedure), except as we approach a 0% infill, because then the weight and role of the shells become non-negligible, so the infill % adjustment is not accurate.

Detailed results: Layer Height test

We printed the specimen with five different layer heights (in mm): 0.10, 0.15, 0.20, 0.25, and 0.30. The other printing parameters are:

Printer: MakerBot Replicator

Speed: 60mm/s

Infill%: 80%

Temperature: 210°C

Infill pattern: Linear

Number of shells: 2

We tested three specimens for each layer height

Considerations on strength

Layer height influences the strength of a printed part when it becomes thin. A printed part at 0.1mm shows a max stress of only 29MPa, as opposed to 35MPa for 0.2mm (21% increase).

Past 0.2mm, the max stress remains fairly constant around 36 MPa (we confirmed this conclusion with an extra test at 0.4mm, not shown here because it was not part of the same batch).

Normalizing max stress by weight smoothens the curve a bit, from 4.7MPa/g at 0.1mm to 5.6MPa/g at 0.3mm. In theory it should show the same evolution as the absolute numbers, because a constant infill should lead to constant weight, regardless of the layer height. But in practice – 3D Matter weighs all specimens – the Replicator adds less material on lower layer heights such as 0.1mm and 0.15mm.

The other result is not surprising: it takes longer to print at lower layer heights, so the max stress divided by printing time shows a curve that is increasing linearly.

Other performance results

As shown on the stress-strain curves, the specimens behave the same way on the first part of the curve: The Young modulus remains constant around 2.9GPa, again well within the range of PLA’s rigidity. And yield stress is also fairly stable around 19MPa.

The curves differ later, for the max stress (as previously seen) and for elongation at break: it increases linearly with layer height, from 2.1% to 3.0%. This is in line with the fact that the material is weaker at lower layer heights, possibly linked to lower accuracy of a thinner deposit.

Detailed results: Infill pattern test

We investigated the properties of five infill patterns: Linear, Diagonal (linear with a 45° tilt), Hexagonal (or honeycomb), Moroccan stars and Catfill The other printing parameters are:

Printer: MakerBot Replicator

Speed: 60mm/s

Layer height: 0.20mm

Temperature: 210°C

Infill%: 10%

Number of shells: 2

We tested three specimens for Linear, Diagonal and Hexagonal, and only one for Moroccan stars and Catfill.

Linear, Diagonal and Hexagonal are all fairly comparable in terms of strength. Linear is ~10% stronger than the other two, but with a fairly wide error bar. Catfill and Moroccan stars are clearly weaker, as we would expect from these suboptimal structures.

It is important to note that the infill % chosen (10%) is very low and does not necessarily extrapolate well for higher infill %. The box on Anisotropy (see later in this section) also compares (for a different purpose)Linear with Diagonal at 100% infill and gives a slightly different conclusion: Diagonal is 10% stronger than Linear. This low infill % was chosen because we realized that 1) Catfill and Moroccan stars are not printable at a high %, and 2) Hexagonal starts looking very similar to Linear past 30% infill.

Elongation at break is between 1.8% and 2.5% but with very wide error bars, so we can consider that it is in the same range of 2%.

In conclusion, while decorative patterns such as Moroccan stars and Catfill show clearly poorer performance, Linear, Diagonal and Hexagonal are comparable at 10% infill.

Box: Anisotropy

What of the anisotropic quality of 3D printing? “Anisotropic” means that the properties of the material depends on the direction considered. The process of 3D printing inherently tends to create weaknesses along the Z-axis, because the interface between layers is not as strong. We printed 9 specimens at 100% infill: 3 in the X direction (=Linear), 3 in the 45°X / 45°Y direction (=Diagonal), and 3 in the Z direction (specimen printed vertically).We found that the Z-axis direction was20% to 30% weaker than other directions, and that max elongation was about half.

Conclusion

Testing the mechanical performance of 3D printed PLA depending on infill %, layer height and infill pattern allowed us to define the trade-offs the user faces when choosing his settings. While the focus of the study was on mechanical performance, we made sure to include quality, cost and speed as key requirements on top of strength for 3D printer users.

Purely on mechanical performance, 3D Matter also found interesting results, such as the fact that elongation at break is lowest around 90% infill, that a lower layer height weakens the object, and that Linear, Diagonal and Hexagonal patterns show fairly equivalent performance.

We also got an interesting data point regarding the difference between printing directions, and while the Z-axis is, as expected, weaker than other directions, the decrease in max stress is only 20-30%.

Disclaimer

We didn’t test printing quality to come up with our recommendations. We took from experience that the quality decreases when the layer height increases. Also, because of the bumpy top layer, 100% infill prints are of lower quality.

We opened several interesting research leads in this paper but some of the results on mechanical performance deserve further investigation to prove hypotheses we formulated – for example regarding the behavior of printed PLA around 90% infill.

We did not investigate the influence of other key printing parameters, in particular extrusion temperature and printing speed.

The specimens were printed without roof or floor, but with two shells. We did not investigate the influence of roof, floor or shell thickness.

This study is valid for PLA, the conclusions might change for other materials such as ABS.

The printing parameters we used and results we got are specific to the Makerbot Replicator. They might be slightly different on other printers.

[1] We measured actual values for strength (max stress), weight and printing time for all infill % at 0.2mm and for all layer heights at 80% infill, and extrapolated the rest of the tables from these values

[2] Infill % does not matter with regard to quality (it is inside) except at 100% infill where we have observed that the prints were not as smooth due to an excessive amount of material extruded

54 Comments

I’m an engineering student researching the mechanical properties of materials manufactured by FDM.

Some results actually surprise me, showing that understanding the behavior of FDM printed objects is quite complex. I expect that the effect of layer height is different when printed at 90% infill, because a smaller layer height will create less voids.

In your Key findings table, you have some duplicate entries with different sets of Xs in the columns. For example, 70% infill and 0.2 layer height is showing twice; one with all 4 columns checked and the other with only Strength and Low Cost. There are a few duplicates in there. Can you please double check that table?

Hi Michael,
The way we set up this table is the other way around: you choose what requirements you would like to have (e.g. I would like strength and quality), and we suggest settings for infill% and layer height (90% infill and 0.15 layer height). We have no duplicate on the left-hand side of the table in the combinations of requirements, but there can be duplicates on the right-hand side if a pair of settings (such as 70% and 0.2 layer height) makes sense in several cases.
Hope this helps!

Extremely interesting study, and thank you for this. I print my cameras exclusively in ABS as PLA deforms in heat, such as a car dashboard. Apart from naturally wanting to see these results replicated for ABS, I understand that repeating these tests for different speed/extruder temperatures would be extraordinarily time consuming, but perhaps you could confine such tests to the Z dimension to reduce the time required. Layer bonding is extremely important – because my cameras are tall, if I don’t get the extrusion temperature high enough, they can crack midbody from internal pressure gradients. A study in vertical layer bonding would be of value to many.

Hi Clint,
Thank you for your message. We are currently testing some ABS filament suppliers so check back in a few weeks and you will get some data on this material. But we have not planned to replicate the study on the influence of parameters for ABS yet (in particular we didn’t plan to make the Z-axis comparison again). We wish we could do a lot more but as you said, it costs us a lot of time and money to do this type of study! However, if you want something tailored to your needs, even a small study, let us know at arthur@my3dmatter.com and maybe we can work something out.

The point was to assess the difference between the Z-axis and the X/Y plane, so we didn’t really look into the difference between 45 degrees and X or Y directions. Will look into it though and let you know if I get an answer!
We are planning to test other materials indeed: ABS will be part of our next study, and nylon and other thermoplastics will be part of a subsequent one.

I have seen at least one other test where 45 degree 100% infill proved to be the strongest. The test piece was a beam and not a direct tensile test but the material was PLA and so relatively brittle compared to ABS etc. In my view the 45 degree infill pattern allows the stresses in the crossed layers to be in indirect tension and shear in a balanced way between the layers. If this is so then less brittle materials would benefit more from 45 degree infill pattern.

Thoroughly enjoyed this! Thanks for the research. A lot of this is intuitive and is somewhat witness able through lots of printing, however seeing the numbers and having someone perform a few good experiments is wonderful. Glad to have found the site through this study. Bookmarked!

Fantastic work! This is the most detailed study I’ve yet seen on this subject!
Actually, I’ve been working on some mechanical testing of my own. I’ve designed an open source (partly 3d printed) testing machine which I will use to determine various other 3d printed characteristics. I plan on using mostly ABS specimens so it will be interesting to compare notes.

I am doing similar research using ABS and some nylon with infused fiber. I was wondering what ASTM standard you used. I a currently using D0638. I had to make some significant alterations to the standard, due to equipment limitations and to encompass my study’s scope.

I am comparing infill settings, build time, material used and build orientation to strength. This info will hopefully help me find the best cost to strength ratio. The odd thing that I have found in my initial data processing is that Young’s Modulus changes drastically from low infill setting to a solid part.

I am currently processing raw data and will soon move onto statistical analysis. Please contact me if you’d like a summary of the research once that is done.

Hi Eric,
We based our procedure on the ISO 527-1 standard, which I believe is the European equivalent of D0638. We also made significant changes to the standard because we needed it to be adapted to 3D printing.
I am a little surprised that your Young Modulus would change if you adjust it to the infill. As we point out in our study, the Young Modulus was constant
for all infills once we divided the raw data by the infill % (except at very low percentages because then the shell’s influence is non-negligible, which skews the calculation).
We would be very happy to get a summary of your research once you’re done!

Yes we could have corrected by subtracting the shell’s area and then dividing by infill %, and we would have certainly found the Young Modulus to be constant even at low infill%.
We thought this was maybe more complicated to explain to the reader, whereas emphasizing that the shell becomes important at low infill % was a good point to make.

This is great, and thank you for sharing. In order to be able to actually use this data, can you tell us the following:

– What model Makerbot was this performed on?
– Which specific ABS and PLA filaments were used?
– Where was the testing done and the specifics of how it was tested (i.e. the equipment, etc.)?
– Who are you and what institution you are affiliated with?

Again. thank you for sharing all of your hard work. These questions are not to criticize or denigrate what you have shared but to be able to understand the experimental method used.

Hi there,
We used a Makerbot 5th Gen to perform all the tests. The tests were conducted exclusively on PLA, with one French filament supplier and one Chinese filament supplier. We tested the specimens on an Instron Universal Testing Machine. 3D Matter is a startup and is not affiliated with any institution. If you are interested in knowing more about us, please contact us directly at arthur@my3dmatter.com
Hope this helps!

[…] I’m curious about are clearly some of the more esoteric material properties. For example, the best study I’ve yet seen on the subject of lattice structure happened to come out last week. It’d say it’s a good start […]

Could you include information on shell thickness for your layer height test please? I believe that strength is more likely controlled by the W/H ratio of the individual shell extrusion lines, number of shells, and total shell thickness rather than layer height.

The problem is that when you vary the layer height, you can’t keep the other variables I mentioned constant. At the very least, either the W/H ratio or total shell thickness will have to change with the layer height.

Hi Loong Jin,
You are making a very good point. We kept the number of shells constant across layer heights, so I agree with you that shell thickness is 2x bigger for 0.2mm than it is for 0.1mm. This can partially explain the increase in strength as layer height increase from 0.1mm to 0.2mm, but if it was the only factor then the tensile strength would keep increasing from 0.2mm to 0.3mm.
From a practical standpoint, we think that users usually set the number of shells once and then vary the layer height, but don’t necessarily adjust the number of shells based on the layer height they pick. So this test may represent what happens in real life better, but I will keep your comment in mind in future studies.

[…] and functional parts (such as tools) are usually between 30-70%. This table taken from this article on my3dmatter.com shows which fill density and layer height would best match the requirements for the final […]

Hi Shubam, not sure what you are asking here but we use a universal testing machine to conduct tensile testing. We measure the max stress that a material can undergo before it breaks (by slowly pulling on it).

Hi,
I wanted to know if you have created any comparison between the results of this test to the mechanical properties of the material manufactured using traditional manufacturing process. If yes, then it would be very helpful for me if you can share the information
thank you.

Hi Rohti, we have not done the tensile testing ourselves on the PLA we are using because it would mean melting the filament and injection molding it (if we want the exact same PLA), but you can get a fairly good comparison to injection molding PLA by comparing it to the datasheets available online. For example, this grade of PLA is a very good comparison:

[…] We already pointed out the influence of infill percentage, layer height and infill pattern in a previous article. The outer surface is another key component of the toolpath, and is one more parameter that makes […]

[…] You can also use higher layers, but in this case, you will lose some quality, so you have to find the right compromise between quality and costs. If you’re interested in learning more about how changing the infill can affect the strength of a 3D printed part, then you should check 3D Matter’s case study on this topic. […]

Nice work guys! I have one commentary about the results of layer heights, because i can agree with your results.

I think, at more layer height will be less interlayer lines that act like cracks that will making the piece more weak. That´s why a minor layer height, the parts will be more weak. I think this only apply to materials with very good interlayer adhesion.

Hi Jose, thank you for your input! We have conducted many more tests on the influence of layer height on other polymers and don’t always reach the same trendlines, maybe your suggestion that it depends on how good the interlayer adhesion is for a given polymer is something to explore…

Slicer now supports 3D honeycomb. Will it change the findings of this study? Or do you expect it to still be equivalent to diagonal/linear?

Also, while on XY I understand that diagonal and linear should be equivalent to HC, I would expect on Z a very different behaviour in compression. 3D honeycomb is meant to extend that advantage to also XY.

Since this study we have designed a new tensile specimen specifically designed to test patterns, and we will try to write soon a brief article about the new results we got and in particular we will include 3D honeycomb in the scope of the work. Meanwhile, you can see our updated results for PLA on our data tool Optimatter. Even the Free Version should enable you to look at the data for different patterns at low infill (set it to 10%-30% to get the biggest differences). 3D Honeycomb is not yet in OptiMatter though, but we will try to add it soon.

Very interesting and nice work. Thanks.
I have a question for you: what is your linear infill pattern? What is your slicing software? I used rectilinear in 0 degree, but I am encountering defects in the areas of changing width due to the nature of tensile bars. Any comments? Thanks.